The original Forza Horizon looks stunning on Xbox One X at 4K

Microsoft restarted its programme of Xbox One X enhancements for Xbox 360 games this week with four new titles - Forza Horizon, The Witcher 2, Crackdown and Fable Anniversary Edition. We're seeing the same 9x resolution boost on all releases in concert with improved performance where appropriate, but it's the first game in this new line-up that's our focus today. Image quality in Forza Horizon is off the charts in the transition to ultra HD and there are a couple of further, surprising enhancements that caught our eye.

One of the last first party exclusives for Xbox 360, Forza Horizon was a landmark title - a successful collaboration between franchise founders Turn 10 and UK-based start-up Playground Games. While retaining its signature 360Hz physics simulation technology, Playground revamped the Forza Motorsport 4 engine, adding time of day lighting based on over 200 variables to FM4's existing, beautiful image-based lighting and its gamma correct pipeline. The open world concept was Playground's idea, and the background streaming tech necessary to create a seamless, vast racing experience came from the Leamington-based studio. It was the beginning of a collaboration that would go on to benefit both studios across a range of racing releases.

What made Forza Horizon's concept possible was switching down Motorsport's 60Hz refresh to the more usual 30 frame per second standard, a performance level that is absolutely locked on both original hardware and indeed Xbox One X. Advanced motion blur attempts to pick up the difference - and despite the arrival of a new 'performance mode' for the X emulator, the truth is it doesn't do a whole lot for this title.

Consistency in frame-rate was built-in to Playground's work from the get-go. Forza Horizon used a careful CPU and GPU budgeting system defined during development and based on worst case scenarios to ensure optimal performance - it's a technique also used by Turn 10 too for its main series entries. The new performance mode opens up the extra GPU power for higher frame-rates rather than pixel-counts, but it cannot exceed limits set by the original game's frame-rate cap. When 30fps is the aim and you hit that target perfectly, the additional overhead can't contribute anything further.

Tom and Rich sit down to discuss their experiences of playing Forza Horizon at native 4K via Xbox One X backwards compatibility - the game looks great.

Our advice? Stick to the standard graphics mode for this one. Microsoft's 'Heutchy Method' - named after the engineer that devised it - increases resolution by a factor of three on both axes, meaning that the original native 720p game renders at the top-end 3840x2160 on Xbox One X. As usual, the emulator employs negative LOD bias to ensure that the highest quality mip-maps are deployed for additional detail, but Playground's original dedication to image quality pays off massively here. The Xbox 360 game uses 4x multi-sampling anti-aliasing (MSAA) in combination with post-process FXAA when GPU resources allow. The end result when blown up to 4K is simply a marvel.

It would be an exaggeration to say that the game holds up compared to its native Xbox One successors, but certain aspects of the presentation still look absolutely pristine. Even at 4K, sub-pixel detail on environmental objects - foliage, specifically - can break up and shimmer in motion. However, with its extreme approach to anti-aliasing, Horizon looks virtually flawless. And if you're running your X console on a 1080p screen, the image quality benefits still further from super-sampling, making for what must surely be one of the most ridiculously comprehensive combinations of anti-aliasing techniques we've seen in a console game. In motion, and paired with the level of detail and wonderful lighting, Forza Horizon on Xbox One X really is something quite special, regardless of the screen you use.

It is a game of its time though - geometry on vehicles and environments received a generational leap from Xbox 360 to Xbox One, while overall detail and the approach to lighting is simply on another level when compared with 2014's Forza Horizon 2. Watching races play out up-close via replays, it's also clear to see that the additional fidelity of the physics simulation provided by Xbox One provides another tremendous boost. According to Playground Games - and indeed the methodology in building X-enhanced 360 games that we discussed recently with the back-compat team - everything that's improved about the game is done at the emulator level. And this begs the question - what's going on with the super high-res fontography in Forza Horizon?

The release of the X-Enhanced Forza Horizon follows the recent native 4K upgrade for FH3 - another beautiful release. We just need a 4K patch for Horizon 2 to complete the set. How about it, Playground Games?

Perhaps the biggest limitation of the X enhancement procedure is that original 2D elements are built for the original 720p presentation, so text and flat art bitmaps are scaled by 9x for a 4K screen, looking indistinct, blurry or blocky depending on the content. Some aspects of this persist in Forza Horizon, but every piece of text seems to be rendered at native resolution. It makes a huge difference to consistency in the 4K presentation, which makes us wonder if a higher quality asset is inserted for X users, or whether higher quality characters were available in the original game. It's hard to believe that Playground would use a vector-based font (which would scale to any resolution) or downscaled a much higher quality font as a matter of course. Regardless, we're glad it's there - it adds further polish to a great presentation.

And crucially, the original Forza Horizon still holds up overall as a great game. It plays well, and the transition to 4K gives us a good excuse to revisit what is still a lovely piece of work - and to witness the beginnings of a franchise off-shoot that would go on to deliver a remarkable level of success on its own terms. Forza Horizon 3 has gone on to become one of the biggest first party hits in the Xbox One line-up, and a couple of months back, it received its own Xbox One X 4K upgrade. And that means we're now left in the position where the still-excellent Forza Horizon 2 is the only series entry you can't play at native ultra HD on Xbox One X - a situation we hope to see resolved in due course. Revisiting the sequel for this article, it remains a visual treat and would look brilliant at full 4K on X hardware.

Forza Horizon is an exceptionally strong release for the X-enhanced back-compat line-up, and we're looking forward to testing the other releases. What we can say is that the tearing in the Witcher 2 is gone and performance has improved, and we're particularly fascinated to see how CD Projekt Red's vast range of engine revamps and optimisations fares at 4K resolution (3840x2016 to be exact, up from the original's 1280x672) and how that all compares to the 4K PC experience. And then there's Fable Anniversary Edition and the classic Crackdown 2 - both blighted by bouts of poor performance on original hardware. Can Xbox One X deliver both the resolution boost and a lock to target frame-rate? Or does the X emulator's performance mode actually find some use here? We'll have answers very soon.